Photodiode array

ABSTRACT

A light receiving region includes a plurality of light detecting sections 10. The light detecting sections 10 has a second contact electrode 4A. The second contact electrode 4A is arranged at a position overlapping a first contact electrode 3A, so as to contact the first contact electrode. Further, a resistive layer 4B is continued to the second contact electrode 4A.

This is a continuation application of copending prior application Ser.No. 14/314,616, filed on Jun. 25, 2014, which is a continuation of priorapplication Ser. No. 13/655,907, filed on Oct. 19, 2012, which is issuedas U.S. Pat. No. 8,791,538. The prior application Ser. Nos. 13/655,907and 14/314,616 are incorporated by reference herein in their entireties.

TECHNICAL FIELD

An aspect of the present invention relates to a photodiode array.

BACKGROUND

A conventional photodiode array is described in, for example, thefollowing Patent Document 1. A photodiode array such as an SiPM (SiliconPhoto Multiplier) or a PPD (Pixelated Photon Detector) has aconfiguration in which APDs (avalanche photodiodes) are arrayed in amatrix state, and the plurality of APDs are connected in parallel, toread out a sum of APD outputs. When the APDs are operated in the Geigermode, it is possible to detect feeble light (photons). That is, in thecase where photons are made incident to an APD, carriers generatedinside the APD are output to the outside via a quenching resistor and awiring pattern for signal readout. Although an electric current flows inthe pixels in which an avalanche effect occurs in the APD, a voltagedrop occurs in the quenching resistor of approximately several hundredsof kΩ, which is directly connected to the pixels. Due to this voltagedrop, a voltage applied to the amplified region of the APD lowers, andthe multiplication action due to the avalanche effect is terminated. Inthis way, one pulse signal is output from an APD by incidence of onephoton. Conventionally, a first contact electrode is provided in one ofthe semiconductor layers composing a p-n junction, and a resistive layeris connected to the wiring in the same plane of the wiring continued tothe first contact electrode.

[Patent Document 1] European Patent Application Publication No.1,755,171.

SUMMARY

However, in the case where a plurality of photons are made incident toan APD at short time intervals, an interval between the output pulsesignals is shortened, to be unable to perform pulse separation, whichmakes it incapable of photon counting. The present invention has beenachieved in consideration of such a problem, and an object of thepresent invention is to provide a high dynamic range photodiode arraywith a high counting rate.

In order to solve the above-described problem, a photodiode arrayaccording to an aspect of the present invention, comprises a lightreceiving region, wherein the light receiving region includes aplurality of light detecting sections, and each of the light detectingsections comprises: a first semiconductor region of a first conductivitytype, a second semiconductor region of a second conductivity type, thesecond semiconductor region forming a p-n junction with the firstsemiconductor region, a first contact electrode being in contact withthe second semiconductor region, a second contact electrode having amaterial different from that of the first contact electrode, the secondcontact electrode being arranged at a position overlapping the firstcontact electrode and being in contact with the first contact electrode,and a resistive layer continued to the second contact electrode.

In the case of the photodiode array according to the present aspect, byarranging the second contact electrode at a position overlapping thefirst contact electrode, it is possible to minimize a space required forthe connection of the resistive layer and the first contact electrode.It is a matter of course that the first contact electrode and the secondcontact electrode are naturally not in the same plane, to be differentin height position, and the resistive layer is continuously extendedfrom the second contact electrode. Thus it is possible to omit wiring inthe light detecting sections, which makes it possible to considerablyincrease an aperture ratio of the light detecting sections.

Carriers generated in the p-n junction by incidence of photons flow inthe resistive layer via the first contact electrode and the secondcontact electrode, to be taken out to the outside via the wiring patternconnected to the resistive layer.

Further, the second contact electrode and the resistive layer preferablyhave SiCr. Because SiCr has high optical transmittance, even when aresistive layer is present in the light detecting sections, incidentphotons are allowed to transmit through the resistive layer, andtherefore, it is possible to increase an effective aperture ratio.

Further, the resistive layer is preferably extended in a curvilinearmanner, to be connected to the wiring pattern for signal readout.Because a resistance value of the resistive layer is proportional to itslength, provided that the resistive layer is extended in a curvilinearmanner, it is possible to increase a resistance value. Further, by thepresence of the resistive layer, it is possible to stabilize a surfacelevel of the semiconductor layer which is present thereunder, tostabilize the outputs.

Further, a thickness of the resistive layer is preferably 3 nm or moreand 50 nm or less. When it is the lower limit or more, it is possible tosecure the uniformity of the resistive layer, and when it is the upperlimit or less, it is possible to allow photons to transmit through theresistive layer sufficiently.

The wiring pattern includes a shape surrounding each of the lightdetecting sections, each of the second contact electrodes is located inthe central area of each light detection region surrounded by the wiringpattern, and a two-dimensional pattern of the resistive layer includes ashape extended so as to turn around the second contact electrode. Byarranging the second contact electrode in the central area of the lightdetection region, so as to turn around the second contact electrode, itis possible to set the length of the resistive layer to be longer.

Further, in the case where photons are made incident to the lightdetecting sections, a recovery time which is stipulated by a period froma clock time of having an intensity peak value of an output from thelight detecting sections to a clock time at which the output from thelight detecting sections reaches 37% of the intensity peak value, may beset to 5 ns or less.

Further, an interval between the centers of the adjacent light detectingsections may be set to 20 μm or less. In this case, the recovery time isconsiderably shortened.

Further, an interval between the centers of the adjacent light detectingsections may be set to 15 μm or less. In this case, the recovery time isfurther shortened.

Further, an interval between the centers of the adjacent light detectingsections may be set to 10 μm or less. In this case, the recovery time isfurthermore shortened.

In accordance with the photodiode according to the aspect of the presentinvention, it is possible to have a high count rate by shortening itsrecovery time.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a photodiode array.

FIG. 2 is a longitudinal sectional view taken along arrows II to II ofthe photodiode array.

FIG. 3 is a graph showing a relationship between the wavelength (nm) andthe transmittance (%) of incident light to SiCr.

FIG. 4 is a diagram showing a photograph of a light detecting sections(arrayed at intervals of 50 μm).

FIG. 5 is a diagram showing a photograph of a light detecting sections(arrayed at intervals of 25 μm).

FIG. 6 is a diagram showing a photograph of a light detecting sections(arrayed at intervals of 20 μm).

FIG. 7 is a diagram showing a photograph of a light detecting sections(arrayed at intervals of 15 μm: Type A).

FIG. 8 is a diagram showing a photograph of a light detecting sections(arrayed at intervals of 15 μm: Type B).

FIG. 9 is a diagram showing a photograph of a light detecting sections(arrayed at intervals of 10 μm).

FIG. 10 is a graph showing a relationship between the wavelength (nm) ofincident light and the detection efficiency (%) of photons.

FIGS. 11A, 11B, 11C, and 11D are graphs showing relationships betweenthe output of photodiode and the time.

FIGS. 12A, 12B, and 12C are diagrams for explanation of a method ofmanufacturing a photodiode.

FIG. 13 is a longitudinal sectional view of a photodiode array in whicha structure of its substrate is changed.

FIG. 14 is a plan view of a photodiode array.

DETAILED DESCRIPTION

Hereinafter, a photodiode array according to an embodiment will bedescribed. In addition, the same reference numerals are to be used forthe same components, and overlapping descriptions will be omitted.

FIG. 1 is a perspective view of a photodiode array, and FIG. 2 is alongitudinal sectional view taken along arrows II to II of thephotodiode array.

This photodiode array has a light receiving region on the surface sideof a semiconductor substrate made of Si. The light receiving regionincludes a plurality of light detecting sections (light detectionchannels) 10, and these light detecting sections 10 aretwo-dimensionally arrayed in a matrix state. In addition, the lightdetecting sections 10 in three rows and in three columns are arrayed,and these compose the light receiving region. Meanwhile, the number ofthe light detecting sections 10 may be larger or smaller, and may beconfigured to be one-dimensionally arrayed.

A wiring pattern (top surface electrode) 3C for signal readout, which issubjected to lattice-shaped patterning, is arranged on the substratesurface. In addition, in FIG. 1, description of an insulating layer 17shown in FIG. 2 is omitted in order to make the internal structureclear. The inside of the apertures of the lattice-shaped wiring pattern3C stipulates light detection regions. The light detecting sections 10are arrayed in the light detection region, and the outputs of the lightdetecting sections 10 are connected to the wiring pattern 3C.

A bottom surface electrode 20 is provided on the substrate rear surface.Accordingly, provided that a driving voltage for the light detectingsections 10 is applied between the wiring pattern 3C serving as the topsurface electrode and the bottom surface electrode 20, it is possible totake out its light detection output from the wiring pattern 3C.

In the p-n junction, the p-type semiconductor region composing the p-njunction composes an anode, and the n-type semiconductor region composesa cathode. In the case where a driving voltage is applied to thephotodiode so as to make an electric potential of the p-typesemiconductor region higher than an electric potential of the n-typesemiconductor region, this is a forward bias voltage, and in the casewhere a driving voltage opposite thereto is applied to the photodiode,this is a reverse bias voltage.

The driving voltage is a reverse bias voltage to be applied to thephotodiode, which is composed of the internal p-n junction in the lightdetecting sections 10. In the case where this driving voltage is set toa breakdown voltage or less of the photodiode, an avalanche breakdownoccurs in the photodiode, and the photodiode is operated in the Geigermode. That is, each photodiode is an avalanche photodiode (APD). Inaddition, in the case where a forward bias voltage is applied to thephotodiode as well, the photodiode has a light detection function.

A resistive part (quenching resistor) 4 which is electrically connectedto one end of the photodiode is arranged on the substrate surface. Oneend of the resistive part 4 composes a contact electrode 4A which iselectrically connected to one end of the photodiode via a contactelectrode of a different material which is located immediately belowthis, and the other end composes a contact electrode 4C which contactsthe wiring pattern 3C for signal readout, to be electrically connectedto the wiring pattern 3C. That is, the resistive parts 4 in therespective light detecting sections 10 are provided with the contactelectrodes 4A connected to the photodiode, the resistive layer 4Bextended in a curvilinear manner so as to be continued to the contactelectrodes 4A, and the contact electrodes 4C continued to the terminalend portion of the resistive layer 4B. In addition, the contactelectrode 4A, the resistive layer 4B, and the contact electrode 4C arecomposed of resistive layers of the same resistance material, and theseare continued to each other.

In this way, the resistive part 4 is extended in a curvilinear mannerfrom the electrical connecting point with the photodiode, to beconnected to the wiring pattern 3C for signal readout. Because aresistance value of the resistive part 4 is proportional to its length,the resistive part 4 is extended in a curvilinear manner, thus it ispossible to increase the resistance value. Further, provided that theresistive part 4 is present, it is possible to stabilize a surface levelof the semiconductor region present under the resistive part 4, tostabilize the output.

In the example shown in FIG. 1, the wiring pattern 3C includes a shapesurrounding each of the light detecting sections 10. However, the shapeof the wiring pattern 3C is not limited to this shape, and for example,the wiring pattern 3C may be formed into a shape surrounding two or moreof the light detecting sections 10, or a shape surrounding one or morecolumns of the light detecting sections 10 (refer to FIG. 14).

In addition, in FIG. 14, a plurality of rows of light detecting sectionsare set as one group, and the wiring of the wiring pattern 3C isextended thereamong.

Further, as shown in FIG. 14, by arranging the resistive layer 4B so asto cover the edge of a semiconductor region 14 in each of the lightdetecting sections 10, it is possible to stabilize a surface level ofthe semiconductor region 14. To describe in detail, the resistive layer4B is arranged on the outline form of the semiconductor region 14, whichis viewed from the thickness direction.

One ends of the photodiodes included in the light detecting sections 10are essentially connected to the wiring pattern 3C of the same electricpotential at all the positions, and the other ends are connected to thebottom surface electrode 20 providing a substrate potential. That is,the photodiodes in all the light detecting sections 10 are connected inparallel.

In addition, in place of the bottom surface electrode 20, a holereaching the semiconductor region 12 from the substrate surface side maybe opened, and the inner face of the hole is coated with an insulatingfilm, to thereafter form a through-silicon via contacting thesemiconductor region 12. However, in order to improve the aperture ratioof the light detecting sections 10, the bottom surface electrode 20 ispreferable to a through-silicon via.

In the example shown in FIG. 1, each of contact electrodes 4A is locatedin the central area of each light detection region surrounded by thewiring pattern 3C. Then, the two-dimensional pattern of the resistivepart 4 includes a shape extended so as to turn around the contactelectrodes 4A. Provided that the contact electrodes 4A are arranged inthe central area of the respective light detection regions, and theresistive layer 4B is arranged so as to turn around the contactelectrodes 4A, it is possible to set the length of the resistive layer4B to be longer.

As shown in FIG. 2, each of the light detecting sections 10 is providedwith a first conductivity type (n-type) first semiconductor region(layer) 12, and a second conductivity type (p-type) second semiconductorregion (a semiconductor layer 13 and a high-impurity concentrationregion 14) composing a p-n junction with the first semiconductor region12.

A first contact electrode 3A contacts the high-impurity concentrationregion (semiconductor region) 14 in the second semiconductor region. Thehigh-impurity concentration region 14 is a diffused region(semiconductor region) formed by diffusing impurities in thesemiconductor layer 13, and has an impurity concentration higher thanthat of the semiconductor layer 13. In this example (Type 1), the p-typesemiconductor layer 13 is formed on the n-type first semiconductorregion 12, and the p-type high-impurity concentration region 14 isformed on the surface side of the semiconductor layer 13. Accordingly,the p-n junction composing the photodiode is formed between thesemiconductor region 12 and the semiconductor layer 13.

In addition, as a layer structure of the semiconductor substrate, astructure in which the conductivity types are reversed from thosedescribed above may be adopted. That is, the structure of (Type 2) isformed such that the n-type semiconductor layer 13 is formed on thep-type first semiconductor region 12, and the n-type high-impurityconcentration region 14 is formed on the surface side of thesemiconductor layer 13.

Further, the p-n junction interface may be formed on the surface layerside. In this case, the structure of (Type 3) is a structure in whichthe n-type semiconductor layer 13 is formed on the n-type firstsemiconductor region 12, and the p-type high-impurity concentrationregion 14 is formed on the surface side of the semiconductor layer 13.

In addition, in the case of this structure, the p-n junction is formedat the interface between the semiconductor layer 13 and thesemiconductor region 14.

It is a matter of course that it is possible to reverse the conductivitytypes in such a structure. That is, the structure of (Type 4) is astructure in which the p-type semiconductor layer 13 is formed on thep-type first semiconductor region 12, and the n-type high-impurityconcentration region 14 is formed on the surface side of thesemiconductor layer 13.

In addition, a structure shown in FIG. 13 may be adopted as a structureof the semiconductor substrate.

FIG. 13 is a longitudinal sectional view of a photodiode array in whicha structure of its substrate is changed.

This structure is different from the structures of Type 1 to Type 4described above in the point that a semiconductor region 15 is arrangedimmediately below the semiconductor region 14, and the other points arethe same as each other. The semiconductor region 15 has the sameconductivity type as that of the semiconductor region 14, or a differentconductivity type therefrom. The semiconductor region 15 having the sameconductivity type is considered as (Type 1S) to (Type 4S), and thesemiconductor region 15 having a different conductivity type isconsidered as (Type 1D) to (Type 4D). In addition, the impurityconcentration in the semiconductor region 15 is lower than the impurityconcentration in the semiconductor region 14. Further, as a p-typeimpurity, B (boron) may be adopted, and as an n-type impurity, P(phosphorus) or As (arsenic) may be adopted.

In addition, the conductivity types, and the preferable ranges ofimpurity concentrations and thicknesses of the respective layers in theabove-described semiconductor structures are as follows.

(Type 1)

The semiconductor region 12 (conductivity type/impurityconcentration/thickness) (n-type/5×10¹¹ to 1×10² cm⁻³/30 to 700 μm)

The semiconductor region 13 (conductivity type/impurityconcentration/thickness) (p-type/1×10¹⁴ to 1×10¹⁷ cm⁻³/2 to 50 μm)

The semiconductor region 14 (conductivity type/impurityconcentration/thickness) (p-type/1×10¹⁸ to 1×10² cm⁻³/10 to 1000 nm)

(Type 2)

The semiconductor region 12 (conductivity type/impurityconcentration/thickness) (p-type/5×10¹¹ to 1×10²⁰ cm⁻³/30 to 700 μm)

The semiconductor region 13 (conductivity type/impurityconcentration/thickness) (n-type/1×10⁴ to 1×10¹⁷ cm⁻³/2 to 50 μm)

The semiconductor region 14 (conductivity type/impurityconcentration/thickness) (n-type/1×10¹⁸ to 1×10²⁰ cm⁻³/10 to 1000 nm)

(Type 3)

The semiconductor region 12 (conductivity type/impurityconcentration/thickness) (n-type/5×10¹¹ to 1×10² cm⁻³/30 to 700 μm)

The semiconductor region 13 (conductivity type/impurityconcentration/thickness) (n-type/1×10¹⁴ to 1×10⁷ cm⁻³/2 to 50 μm)

The semiconductor region 14 (conductivity type/impurityconcentration/thickness) (p-type/1×10¹⁸ to 1×10²⁰ cm⁻³/10 to 1000 nm)

(Type 4)

The semiconductor region 12 (conductivity type/impurityconcentration/thickness) (p-type/5×10 to 1×10²⁰ cm⁻³/30 to 700 μm)

The semiconductor region 13 (conductivity type/impurityconcentration/thickness) (p-type/1×10¹⁴ to 1×10¹⁷ cm⁻³/2 to 50 μm)

The semiconductor region 14 (conductivity type/impurityconcentration/thickness) (n-type/1×10¹⁸ to 1×10²⁰ cm⁻³/10 to 1000 nm)

(Type 1S)

The parameters of the semiconductor regions 12, 13, and 14 are the sameas those of Type 1.

The semiconductor region 15 (conductivity type/impurityconcentration/thickness) (p-type/1×10¹⁴ to 1×10¹⁷ cm⁻³/2 to 50 μm)

(Type 2S)

The parameters of the semiconductor regions 12, 13, and 14 are the sameas those of Type 2.

The semiconductor region 15 (conductivity type/impurityconcentration/thickness) (n-type/1×10¹⁴ to 1×10¹⁷ cm⁻³/2 to 50 μm)

(Type 3S)

The parameters of the semiconductor regions 12, 13, and 14 are the sameas those of Type 3.

The semiconductor region 15 (conductivity type/impurityconcentration/thickness) (p-type/1×10¹⁴ to 1×10¹⁷ cm⁻³/2 to 50 μm)

(Type 4S)

The parameters of the semiconductor regions 12, 13, and 14 are the sameas those of Type 4.

The semiconductor region 15 (conductivity type/impurityconcentration/thickness) (n-type/1×10⁴ to 1×10¹⁷ cm⁻³/2 to 50 μm)

(Type 1D)

The parameters of the semiconductor regions 12, 13, and 14 are the sameas those of Type 1.

The semiconductor region 15 (conductivity type/impurityconcentration/thickness) (n-type/1×10¹⁴ to 1×10⁷ cm⁻³/2 to 50 μm)

(Type 2D)

The parameters of the semiconductor regions 12, 13, and 14 are the sameas those of Type 2.

The semiconductor region 15 (conductivity type/impurityconcentration/thickness) (p-type/1×10¹⁴ to 1×10¹⁷ cm⁻³/2 to 50 μm)

(Type 3D)

The parameters of the semiconductor regions 12, 13, and 14 are the sameas those of Type 3.

The semiconductor region 15 (conductivity type/impurityconcentration/thickness) (n-type/1×10¹⁴ to 1×10¹⁷ cm⁻³/2 to 50 μm)

(Type 4D)

The parameters of the semiconductor regions 12, 13, and 14 are the sameas those of Type 4.

The semiconductor region 15 (conductivity type/impurityconcentration/thickness) (p-type/1×10¹⁴ to 1×10¹⁷ cm⁻³/2 to 50 μm)

In addition, in the above-mentioned example, the lowermost semiconductorregion 12 composes the semiconductor substrate having a wide thickness.Meanwhile, the light detecting sections 10 may be further provided witha semiconductor substrate under the semiconductor region 12, and in thiscase, the semiconductor region 12 is to have a thickness thinner thansuch an additional semiconductor substrate.

Further, the semiconductor region 13 may be formed on the semiconductorregion 12 by an epitaxial growth method. Meanwhile, the semiconductorregion 13 may be formed by impurity diffusion or ion implantation withrespect to the substrate. The semiconductor regions 14 and 15 may beformed by impurity diffusion or ion implantation with respect to thesemiconductor region 13.

Next, the contact electrode 3A and the resistive part 4 shown in FIGS.1, 2, and 13 will be described.

The respective light detecting sections 10 are provided with aninsulating layer 16 formed on the surface of the semiconductorsubstrate. The surfaces of the semiconductor region 13 and thesemiconductor region 14 are coated with the insulating layer 16. Theinsulating layer 16 has a contact hole, and the contact electrode 3A isformed in the contact hole. The contact electrode 3A in this example ismade of the same material as that of the wiring pattern 3C, and isformed on the insulating layer 16 through the same process. The contactelectrode 3A and the wiring pattern 3C are made of metal, which isspecifically aluminum (Al). Another low-resistance metal material (Au,Ag, Cu) may be used as a material for the contact electrode 3A and thewiring pattern 3C, and a structure of two or more layers or an alloy maybe adopted. As an alloy, for example, a compound containing some of themetallic elements such as Al, Ag, Au, Ge, Ni, Cr, and Ti may be used.

An upper insulating layer 17 is formed on the lower insulating layer 16and the first contact electrode 3A. The insulating layers 16 and 17 aremade of inorganic insulators having high heat resistance such as SiO₂ orsilicon nitride (SiNx). The insulating layer 17 has a contact holearranged coaxially with the first contact electrode 3A, and a secondcontact electrode 4A is formed in the contact hole. Accordingly, thefirst contact electrode 3A and the second contact electrode 4A arecoaxially-arranged.

The second contact electrode 4A contains a material different from thefirst contact electrode 3A. Further, the second contact electrode 4A isa part of the resistive part 4, and has a resistivity higher than thatof the first contact electrode 3A. The second contact electrode 4A isarranged at a position overlapping the first contact electrode 3A, so asto contact the first contact electrode 3A. The resistive layer 4B iscontinued to the second contact electrode 4A.

By coaxially-arraying the second contact electrode 4A at a positionoverlapping the first contact electrode 3A, it is possible to minimize aspace required for the connection of the resistive layer 4B and thefirst contact electrode 3A. It is a matter of course that the firstcontact electrode 3A and the second contact electrode 4A are naturallynot in the same plane, to be different in height position, and theresistive layer 4B is continuously extended from the second contactelectrode 4A.

Thus it is possible to omit wiring in the light detecting sections 10,which makes it possible to considerably increase an aperture ratio ofthe light detecting sections.

In addition, the contact electrode 4C is located at the terminal end ofthe resistive layer 4B. The contact electrode 4C as well is a part ofthe resistive part 4. The wiring pattern 3C formed on the insulatinglayer 16 is located immediately below the contact electrode 4C, and thecontact electrode 4C contacts the wiring pattern 3C, to be connected tothe wiring pattern 3C.

Carriers generated in the p-n junction by incidence of photons flow inthe resistive layer 4B via the first contact electrode 3A and the secondcontact electrode 4A, and are taken out to the outside via the wiringpattern 3C connected to the resistive layer 4B via the contact electrode4C.

The contact electrodes 4A and 4C, and the resistive layer 4B are made ofthe same resistance material. Meanwhile, these may be made of differentmaterials. A single semiconductor, or an alloy or a compound containinga semiconductor and metal in an appropriate ratio may be used as aresistance material. For example, as a resistive element, NiCr, TaNi,FeCr, or the like may be cited in addition to SiCr.

It is a matter of course that the contact electrodes 4A and 4C, and theresistive layer 4B are preferably made of SiCr. Because SiCr has highoptical transmittance, even when a resistive layer is present in thelight detecting sections 10, because incident photons are allowed totransmit through the resistive layer 4B, it is possible to increase aneffective aperture ratio. In addition, wafer in-plane variation inresistance value of SiCr is small, and it is possible to easily thin itby approximately 1 mm. Further, it is possible to heighten sheetresistance.

A sheet resistance of polysilicon is 1 to 30 (kΩ/sq.). Meanwhile, asheet resistance of SiCr is 1 to 50 (kΩ/sq.). That is, provided thatSiCr is used, it is possible to achieve a high resistance value with asmall size.

The thickness of the resistive layer 4B is preferably 3 nm or more and50 nm or less. When it is the lower limit or more, it is possible tosecure the uniformity of the resistive layer, and when it is the upperlimit or less, it is possible to allow photons to transmit through theresistive layer sufficiently.

FIG. 3 is a graph showing a relationship between the wavelength (nm) andthe transmittance (%) of incident light to SiCr composing the resistivelayer. The thickness of this SiCr is 20 nm.

SiCr has transmittance of 80% or more with respect to light with awavelength of 400 nm or more. SiCr has a trend toward blocking of lightwith a wavelength less than 400 nm. In accordance with the graph, asmall spectral peak is shown with respect to the light with a wavelengthof 400 nm or more and less than 500 nm. This means that it is possibleto selectively allow the light with a wavelength of 400 nm or more andless than 500 nm to transmit through even when the light of 500 nm ormore is blocked by a filter. Provided that such a filter is notcombined, it is possible to allow light with a wavelength of 400 nm ormore, at least light with a wavelength up to 1200 nm to transmit throughat transmittance of 80% or more.

The above-described photodiode array was manufactured.

The manufacturing conditions are as follows.

(1) The structure (numerical samples in the structure in FIGS. 1 and 2)

The semiconductor 12:

Conductivity type: n-type (impurity: Sb (antimony))

Impurity concentration: 5.0×10¹¹ cm⁻³

Thickness: 650 μm

The semiconductor 13:

Conductivity type: p-type (impurity: B (boron))

Impurity concentration: 1.0×10¹⁴ cm¹³

Thickness: 30 μm

The semiconductor 14:

Conductivity type: p-type (impurity: B (boron))

Impurity concentration: 1.0×10¹⁸ cm⁻³

Thickness: 1000 nm

The insulating layer 16: SiO₂ (thickness: 1000 nm)

The insulating layer 17: SiO₂ (thickness: 2000 nm)

The contact electrode 3A: (aluminum (Al))

Contact hole diameter: 2.0 μm

The wiring pattern 3C: (aluminum (Al))

Thickness: 1.0 μm

Width W0 of the wiring pattern 3C: 1.0 to 3.0 μm

Area S of the region (light detection region) surrounded by the wiringpattern 3C in the one light detecting sections 10: 100 to 2500 μm²

Interval X between the centers of the adjacent light detecting sections10: 50 μm to 10 μm

The resistive part 4: SiCr

(The Contact Electrode 4A)

Contact hole diameter: 1.0 μm

(The Resistive Layer 4B)

Thickness of the resistive layer 4B: 20 nm

Width W1 of the resistive layer 4B: 1.0 to 3.0 μm

Length L1 of the resistive layer 4B: 10 to 50 μm

Resistance value of the resistive part 4: 200 to 500 kΩ

(The Contact Electrode 4C)

Contact hole diameter: 1.0 μm

(2) Conditions of Manufacturing Process

The semiconductor region 12: Czochralski method ((001) Si semiconductorsubstrate)

The semiconductor region 13: Si epitaxial growth method (raw materials:gas-phase silicon tetrachloride (SiCl₄), trichlorosilane (SiHC₃), growthtemperature of 1200° C.)

The semiconductor region 14: Impurity thermal diffusion method (impurityraw material: diborane (B₂H₆), diffusion temperature of 1200° C.)

The insulating layer 16: (Si thermo-oxidative method: oxidizingtemperature (1000° C.))

The insulating layer 17: (Plasma CVD method: raw material gas(tetraethoxysilane (TEOS) and oxygen gas): growth temperature (200° C.))

The contact electrode 3A and the wiring pattern 3C: Vapor-depositiontechnique (raw material: aluminum)

The resistive part 4: Sputtering method (target material: SiCr)

FIG. 4 is a diagram showing a photograph of the manufactured lightdetecting sections 10 (an interval X between the adjacent centers=50μm).

The parameters of the structure in this example are as follows. Inaddition, the length of the resistive layer 4B is a length of the centerline in the width direction.

Width W0 of the wiring pattern 3C=2.0 μm

Area S of the light detection region=2025 μm²

Width W1 of the resistive layer 4B=3.0 μm

Length (total length) L1 of the resistive layer 4B=200 μm

Resistance value of the resistive part 4=160 kΩ

The shape of the resistive layer 4B is formed annularly as a whole alongthe inner side surface of the lattice-shaped wiring pattern 3C. In thisstructure, the resistive layer 4B has two channels from the position ofthe second contact electrode 4A to the contact electrode 4C for signaloutput. That is, the resistive layer 4B has a resistive layer 4B 1having a relatively short length, and a resistive layer 4B2 having arelatively long length. A resistance value of the resistive layer 4B isgiven as a combined resistance of these resistive layer 4B1 andresistive layer 4B2 having different lengths.

The contact electrodes 4C are arranged at the intersection points of thelattice-shaped wiring pattern 3C. Accordingly, the contact electrodes 4Care located at the four places on the diagonals of the light detectionregion, and the intersection point of these diagonals is the center(center of gravity) G of the light detection region (light detectingsections). A distance X between the centers G of the adjacent lightdetecting sections is 10 is 50 μm.

The resistive layers 4B1 and 4B2 express a substantially rectangularannular shape as a whole, and the shapes of those corners are smoothlycurved. The centers of curvature O of the outer edges of the corners ofthe resistive layers 4B1 and 4B2 are located on the above-mentioneddiagonals passing through the center G, and the radii of curvature R are5.0 μm, and the angles θ formed by the two chords extended from the bothends of the outer edge arcing toward the centers of curvature O are 8°.In addition, the radii of curvature R are set to 2 to 10 μm in order toavoid electric field concentration, and the angles θ are set to 3 to14°.

The carriers taken out of the second contact electrode 4A reach thecontact electrode 4C via the resistive layer 4B, to be taken out to theoutside via the wiring pattern 3C.

FIG. 5 is a diagram showing a photograph of the manufactured lightdetecting sections 10 (an interval X between the adjacent centers=25μm).

The parameters of the structure in this example are as follows.

Width W0 of the wiring pattern 3C=1.5 μm

Area S of the light detection region=420 μm²

Width W1 of the resistive layer 4B=3.0 μm

Length L1 of the resistive layer 4B=70 μm

Resistance value of the resistive part 4=250 kΩ

The shape of the resistive layer 4B is formed, as a whole, into a shapein which a part of a ring is void, along the inner side surface of thelattice-shaped wiring pattern 3C. In this structure, the resistive layer4B has one channel from the position of the second contact electrode 4Ato the contact electrode 4C for signal output.

The contact electrodes 4C are arranged at the intersection points of thelattice-shaped wiring pattern 3C. Accordingly, the contact electrodes 4Care located at the four places on the diagonals of the light detectionregion, and the intersection point of these diagonals is the center(center of gravity) G of the light detection region (light detectingsections). A distance X between the centers G of the laterally-adjacentlight detecting sections 10 is 25 μm.

The resistive layer 4B has three corners composing a part of the ringshape, and the shapes of the respective corners are smoothly curved. Thecenters of curvature O of the outer edges of the corners of theresistive layer 4B are located on the above-mentioned diagonals passingthrough the center G, and the radii of curvature R are 5.0 μm, and theangles θ formed by the two chords extended from the both ends of theouter edge arcing toward the centers of curvature O are 8°. In addition,the radii of curvature R are set to 2 to 10 μm in order to avoidelectric field concentration, and the angles θ are set to 6 to 37°.

The carriers taken out of the second contact electrode 4A reach thecontact electrode 4C via the resistive layer 4B, to be taken out to theoutside via the wiring pattern 3C.

FIG. 6 is a diagram showing a photograph of the manufactured lightdetecting sections 10 (an interval X between the adjacent centers=20μm).

The parameters of the structure in this example are as follows.

Width W0 of the wiring pattern 3C=1.5 μm

Area S of the light detection region=240 μm²

Width W1 of the resistive layer 4B=2.0 μm

Length L1 of the resistive layer 4B=55 μm

Resistance value of the resistive part 4=300 kΩ

The basic structure of the light detecting sections is the same as thatshown in FIG. 5, and overlapping descriptions will be omitted. Adistance X between the centers G of the adjacent light detectingsections 10 is 20 μm. As a different point, in the case of that shown inFIG. 6, the proportion of the contact electrode 4A projecting toward theinside of the light detection region to the width W1 of the resistivelayer 4B is higher than that in FIG. 5. In addition, in the lightdetecting sections in any embodiment, the centers of the contactelectrodes 4A and 4C are concave. A distance between the wiring pattern3C adjacent to the contact electrode 4C and the center position of thecontact electrode 4A is longer than a distance from the wiring pattern3C to the inner edge line of the resistive layer 4B.

The resistive layer 4B has three corners composing a part of the ringshape, and the shapes of the respective corners are smoothly curved. Thecenters of curvature O of the outer edges of the corners of theresistive layer 4B are located on the above-mentioned diagonals passingthrough the center G, and the radii of curvature R are 3.0 μm, and theangles θ formed by the two chords extended from the both ends of theouter edge arcing toward the centers of curvature O are 130. Inaddition, the radii of curvature R are set to 2 to 5 μm in order toavoid electric field concentration, and the angles θ are set to 8 to230.

The carriers taken out of the second contact electrode 4A reach thecontact electrode 4C via the resistive layer 4B, to be taken out to theoutside via the wiring pattern 3C.

FIG. 7 is a diagram showing a photograph of the manufactured lightdetecting sections (an interval X between the adjacent centers=15 μm:Type A). In the light detecting sections of Type A, the contactelectrode 4A is arranged in the center of the light detection region,and the resistive layer 4B is provided with a forward turning region 4Baextended so as to turn clockwise from the center, and a reverse turningregion 4Bb extended so as to turn counterclockwise continuously from theforward turning region 4Ba. In addition, here, a clockwise turning isconsidered as a forward turning. It is a matter of course that it ispossible to manufacture one having a structure in which acounterclockwise turning is considered as a forward turning.

The parameters of the structure in this example are as follows.

Width W0 of the wiring pattern 3C=1.2 μm

Area S of the light detection region=132 μm²

Width W1 of the resistive layer 4B=1.0 μm

Length L1 of the resistive layer 4B=78 μm

Resistance value of the resistive part 4=600 kΩ

The contact electrodes 4C are arranged at the intersection points of thelattice-shaped wiring pattern 3C, and the contact electrodes 4C arelocated at the four places on the diagonals of the light detectionregion. The intersection point of these diagonals is the center (centerof gravity) G of the light detection region (light detecting sections).A distance X between the centers G of the adjacent light detectingsections 10 is 15 μm.

As described above, the resistive layer 4B is provided with the forwardturning region 4Ba and the reverse turning region 4Bb. In thisstructure, the resistive layer 4B has one channel from the position ofthe second contact electrode 4A to the contact electrode 4C for signaloutput. However, the direction of the magnetic field at the center Gformed by the respective regions 4Ba and 4Bb having different turningdirections is reversed. That is, this light detecting sections has astructure in which the effect by the magnetic field formed due to theprogress of detected electrons is balanced out at the center position,thereby reducing the effect on detected output by the self-formingmagnetic field.

The forward turning region 4Ba has gently-curved three corners. Thecenters of curvature Oa1, Oa2, and Oa3 of the outer edges of therespective corners are located on the above-mentioned diagonals passingthrough the center G, and the respective radii of curvature Ra are 2.0μm, and the angles θa formed by the two chords extended from the bothends of the respective outer edge arcing toward the respective centersof curvature Oa1, Oa2, and Oa3 are 190. In addition, with respect to theforward turning region 4Ba, the radii of curvature Ra of the corners areset to 2 to 5 μm in order to avoid electric field concentration, and theangles θa are set to 19 to 580.

The reverse turning region 4Bb as well has gently-curved three corners,and the respective corners have the same shape other than its direction.To describe one angle, the centers of curvature Ob of the outer edge ofthe corner are located on the above-mentioned diagonals passing throughthe center G, and the radius of curvature Rb is 2.0 μm, and the angle θbformed by the two chords extended from the both ends of the outer edgearcing toward the respective centers of curvature Ob is 80. In addition,with respect to the reverse turning region 4Bb, the radius of curvatureRb of the corner is set to 2 to 5 μm in order to avoid electric fieldconcentration, and the angle θb is set to 8 to 230.

In addition, for the reason that the forward turning region 4Ba islocated internally than the reverse turning region 4Bb, the angle θa isset to be greater than the angle θb.

The outer edge of the forward turning region 4Ba located internally andthe inner edge of the reverse turning region 4Bb located externally faceeach other. The minimum value D1 as a distance spaced between these is0.6 μm. The minimum value D1 as a spaced distance is set to 0.6 to 2.0μm.

The carriers taken out of the second contact electrode 4A reach thecontact electrode 4C via the resistive layer 4B, to be taken out to theoutside via the wiring pattern 3C.

FIG. 8 is a diagram showing a photograph of the manufactured lightdetecting sections (an interval X between the adjacent centers=15 μm:Type B).

In the light detecting sections of Type B, the contact electrode 4A isarranged in the center of the light detection region, and the resistivelayer 4B is provided with a turning region extended so as to turn in onedirection from the center. It is a matter of course that it is possibleto manufacture the light detecting sections having a structure in whichthe turning direction is the reverse direction in any one of theembodiments.

The parameters of the structure in this example are as follows.

Width W0 of the wiring pattern 3C=1.2 μm

Area S of the light detection region=132 μm²

Width W1 of the resistive layer 4B=1.0 μm

Length L1 of the resistive layer 4B=55 μm

Resistance value of the resistive part 4=420 kM

The contact electrodes 4C are arranged at the intersection points of thelattice-shaped wiring pattern 3C, and the contact electrodes 4C arelocated at the four places on the diagonals of the light detectionregion. The intersection point of these diagonals is the center (centerof gravity) G of the light detection region (light detecting sections).A distance X between the centers G of the adjacent light detectingsections 10 is 15 μm.

The resistive layer 4B has gently-curved three corners. The centers ofcurvature O of the outer edges of the respective corners are located onthe above-mentioned diagonals passing through the center G, and therespective radii of curvature R are 2.0 μm, and the angles θ formed bythe two chords extended from the both ends of the respective outer edgearcing toward the respective centers of curvature O are 8°. In addition,the radii of curvature R of the corners are set to 2 to 5 μm in order toavoid electric field concentration, and the angles θ are set to 8 to23°.

The carriers taken out of the second contact electrode 4A reach thecontact electrode 4C via the resistive layer 4B, to be taken out to theoutside via the wiring pattern 3C.

FIG. 9 is a diagram showing a photograph of the manufactured lightdetecting sections (an interval X between the adjacent centers=10 μm).The basic structure of the light detecting sections 10 is the same asthat shown in FIG. 8, and descriptions of the same structure will beomitted.

The parameters of the structure in this example are as follows.

Width W0 of the wiring pattern 3C=1.2 μm

Area S of the light detection region=42 μm²

Width W1 of the resistive layer 4B=1.0 μm

Length L1 of the resistive layer 4B=29 μm

Resistance value of the resistive part 4=700 kΩ

In this structure as well, the carriers taken out of the second contactelectrode 4A reach the contact electrode 4C via the resistive layer 4B,to be taken out to the outside via the wiring pattern 3C.

In addition, in this example, despite the fact that the width W1 of theresistive layer 4B is less than the width W0 of the wiring pattern 3C,and the resistive part 4 is miniaturized, it is possible to obtain asufficient resistance value.

Next, the characteristics of the photodiode will be described.

FIG. 10 is a graph showing a relationship between the wavelength (nm) ofincident light and the detection efficiency (%) of photons in theabove-mentioned photodiode. The graph shows the data of the structure ofFIG. 4 (an interval of 50 μm), the structure of FIG. 7 (an interval of15 μm), and the structure of FIG. 9 (an interval of 10 μm). In addition,the numbers of the light detecting sections included in one photodiodearray are respectively 400, 4489, and 1000. A reverse bias voltage tothe photodiode is 74V, and the photodiode was operated in the Geigermode. In addition, a breakdown voltage is 71V.

With respect to the photon detection efficiency (PDE) (%), the largerthe light detection region is, the less the shadow region by theresistive layer is, and the higher the detection efficiency is obtained.However, despite the fact that the area of the light detection regionwhen an interval between adjacent light detection regions is 10 μm isabout one twenty-fifth the area of the light detection region when aninterval between adjacent light detection regions is 50 μm, thedetection efficiency is maintained at 30% or more thereof. In the sameway when an interval between adjacent light detection regions is 15 μm,the detection efficiency is maintained at a relatively high percentage.

The positions of these spectral peaks are present within a wavelengthrange from 400 nm to 500 nm. Within this wavelength range (400 nm ormore and 500 nm or less), in the case of the photodiode at intervals of50 μm, the detection efficiency is 44% or more, and in the case of thephotodiode at intervals of 15 μm, the detection efficiency is 36% ormore, and in the case of the photodiode at intervals of 10 μm, thedetection efficiency is 17% or more.

In addition, as a comparison example 1, with an interval X betweenadjacent centers=50 μm, a first contact electrode was provided at aninner position of the resistive layer in FIG. 4, and an annular wiringpattern (aluminum) which has substantially the same shape as, but isslightly smaller than that of the resistive layer 4B was formed from thefirst contact electrode. In addition, this annular wiring pattern(overhanging electrode) is located on the outline form of thesemiconductor region 14, and has a function of stabilizing a surfacelevel in the light detection region. Then, in the case where a resistiveelement (polysilicon: 160 kΩ) continued to the annular wiring pattern,with the same width of the annular wiring pattern, is formed in the sameway as that shown in FIG. 4, the detection efficiency (%) was 44% atminimum, and was 52% at maximum within the wavelength range from 400 nmto 500 nm. In addition, in the structure of the comparison example 1,the position of the first contact electrode and the connecting positionwith the annular wiring pattern of the resistive element are shiftedfrom each other.

Further, as a comparison example 2, with an interval X in the comparisonexample 1=15 μm, a first contact electrode was provided at an innerposition of the resistive layer in FIG. 8, and an annular wiring pattern(aluminum) which has substantially the same shape as, but is slightlysmaller than that of the resistive layer 4B was formed from the firstcontact electrode. In addition, this annular wiring pattern (overhangingelectrode) is located on the outline form of the semiconductor region14, and has a function of stabilizing a surface level in the lightdetection region. Then, in the case where a resistive element(polysilicon: 500 kΩ) continued to the annular wiring pattern, with thesame width of the annular wiring pattern, is formed in the same way asthat shown in FIG. 8, the detection efficiency (%) was 36% at minimum,and was 42% at maximum within the wavelength range from 400 nm to 500nm. In addition, in the structure of the comparison example 2, theposition of the first contact electrode and the connecting position withthe annular wiring pattern of the resistive element are shifted fromeach other.

In addition, because the position of the first contact electrode and theconnecting position with the annular wiring pattern of the resistiveelement are shifted from each other, it is difficult to set an intervalX=10 μm or less in view of the manufacturing process.

In the structures of the comparison examples 1 and 2, all the annularwiring patterns and resistive parts having low optical transmittancefunction as light blocking components to reduce an active apertureratio, and the light detection sensitivity is lowered. On the otherhand, in the photodiode array according to the embodiment, because theresistive layer 4B has high optical transmittance while achieving thesame surface level stabilizing function as that of the annular wiringpattern, and further, an additional resistive element such aspolysilicon is not used, it is possible to considerably improve thelight detection sensitivity.

Next, an inspection with respect to an effect by a recovery time(voltage recovery time) was carried out.

FIGS. 11A to 11D are graphs showing relationships between the output (inthe Geiger mode) from the above-mentioned photodiode and the time. Thegraphs show the output images on an oscilloscope, and the vertical axesshow the output intensity (gain) of the photodiode, and an interval inthe vertical axis denotes 50 mV, and an interval in the horizontal axisdenotes 5 (ns). On the graphs, multiple data having different peakintensity voltages are shown. However, this is due to a difference inthe number of photons made incident to the photodiode, and the largerthe number of photons is, the higher the output intensity becomes. Onthe graphs, a bias voltage of 73 (V) is applied. In addition, ΔV=biasvoltage to the photodiode-breakdown voltage of the photodiode is withina range of ΔV=1 (V) or more and 4 (V) or less.

In the case where photons are made incident to the light detectingsections 10, a recovery time (τ) of an output signal from the photodiodeis stipulated by a period from a clock time of having an intensity peakvalue of an output from the light detecting sections 10 to a clock timeat which the output from the light detecting sections 10 reaches 37% ofthe intensity peak value.

In the case (FIG. 11A) of an interval X between the light detectingsections=50 μm (FIG. 4), when a bias voltage to the photodiode is 73 V,the recovery time (τ) is 13 ns.

In the case (FIG. 11B) of an interval X between the light detectingsections=20 μm (FIG. 6), when a bias voltage to the photodiode is 73 V,the recovery time (τ) is 5.0 ns.

In the case (FIG. 11C) of an interval X between the light detectingsections=15 μm (Type A: FIG. 7), when a bias voltage to the photodiodeis 73 V, the recovery time (τ) is 4.3 ns.

In the case (FIG. 11D) of an interval X between the light detectingsections=10 μm, when a bias voltage to the photodiode is 73 V, therecovery time (i) may be 2.3 ns or less.

In addition, in the case of the above-mentioned comparison example 1,the recovery time (τ) was 13 ns, and in the case of the above-mentionedcomparison example 2, the recovery time (τ) was 5.0 ns.

To describe in detail, in the case of the structure of the comparisonexample 1 (an interval X of a space between the light detecting sections10=50 μm), the aperture ratio is 60%, the junction capacitance Cj=80 fF,the gain=7.5×10⁵, the recovery time is 13 ns, the pixel count density(400 pixels/mm²), and the photon detection efficiency is 52% at maximum.

Further, in the case of the structure of the comparison example 2 (aninterval X of a space between the light detecting sections 10=15 μm),the aperture ratio is 55%, the junction capacitance Cj=11 fF, thegain=2.0×10, the recovery time is 4.3 ns, the pixel count density (4489pixels/mm²), and the photon detection efficiency is 42% at maximum.

In addition, in the case of X=15 μm, in the structures of the embodimentof FIGS. 7 and 8, the aperture ratio may be set to 60%, the junctioncapacitance Cj=11 fF, the gain=2.0×10⁵, the recovery time is 4.3 ns, andthe pixel count density (4489 pixels/mm²).

In this way, in the structure of the embodiment, while achieving thesame aperture ratio as that of the comparison example 1, it is possibleto reduce the junction capacitance Cj, and to shorten the recovery time.Further, because the pixel count included per unit area is large, it ispossible to improve the dynamic range.

As described above, in the case where an interval X of adjacent secondcontact electrodes (an interval between the centers of the lightdetecting sections) is 20 μm or less, the recovery time (τ) isconsiderably shortened. When an interval X between the light detectingsections is 15 μm or less, it is possible to make the recovery time (τ)10 ns or less. When an interval X is set to 10 μm or less, the recoverytime (τ) is further shortened. This is remarkable improvement which hasnot been achieved conventionally.

As described above, in the photodiode array according to the embodiment,by utilizing the high transmittance of the metal thin film resistor, anoverhanging structure is formed of the metal thin film resistorsubjected to linear patterning in place of the overhanging electrodeused in the comparison examples 1 and 2, to reduce a dead space. Inorder to obtain a desired resistance value, in the case of thestructures shown in FIGS. 5 to 9, it is impossible to coat a portion(the position in the right corner) of the outline form (edge) of thesemiconductor region 14 with the resistive layer 4B. However, thisportion is about the width of the resistive layer 4B, which has a smalleffect on deterioration in characteristics with respect to stabilizationof surface level. Further, in the structure shown in FIG. 4, all theoutline form (edge) of the semiconductor region 14 is coated.

FIGS. 12A to 12C are diagrams for explaining a method of manufacturingthe photodiode array shown in FIGS. 1 and 2.

First, as shown in FIG. 12A, a semiconductor region 13 is formed on thesemiconductor region (semiconductor substrate) 12 by an epitaxial growthmethod, an impurity diffusion method, or an ion implantation method. Inaddition, the semiconductor region 12 is a semiconductor substrate of(100) Si formed by the Czochralski method or the floating zone method.However, a semiconductor substrate having another plane orientation maybe used. In the case where an Si epitaxial growth method is used, forexample, gas-phase silicon tetrachloride (SiCl₄) and trichlorosilane(SiHCl₃) are used as raw materials, and those gases are made to flow onthe substrate surface at a growth temperature of 1200° C. In the case ofan impurity diffusion method, impurities corresponding to theconductivity type of the semiconductor region 13 are diffused as gas orsolid in the semiconductor region 12. In the case of an ion implantationmethod, impurities corresponding to the conductivity type of thesemiconductor region 13 are ion-implanted into the semiconductor region12.

Next, the semiconductor region 14 is formed on the region on the surfaceside of the semiconductor region 13. For this, an impurity diffusionmethod or an ion implantation method may be used. For example, in thecase where diborane (B₂H₆) is used as a raw material in a diffusionmethod, the diffusion temperature may be set to 1200° C. In theformation of the semiconductor region 14, first, a resist pattern havingan aperture is formed on the semiconductor region 13 by a technique ofphotolithography, and next, impurity addition is carried out with thisresist pattern serving as a mask. In addition, after the lattice-shapedwiring pattern 3C is formed, impurity addition may be carried out withthis lattice-shaped wiring pattern 3C serving as a mask via theinsulating layer 16 by an ion implantation method.

Next, the insulating layer 16 is formed on the semiconductor substrate.The insulating layer 16 may be formed by use of an Si thermal oxidationmethod. The oxidizing temperature is, for example, 1000° C. Thus, thesurfaces of the semiconductor regions 13 and 14 are oxidized, to formthe insulating layer 16 made of SiO₂. A CVD method may be used for theformation of the insulating layer 16.

Next, a contact hole is formed at a position on the semiconductor region14 in the insulating layer 16. In the formation of the contact hole,first, a resist pattern having an aperture is formed on the insulatinglayer 16 by a technique of photolithography, and next, the insulatinglayer 16 is etched with this resist pattern serving as a mask. As anetching method, in addition to a dry etching method, wet etching with anetchant containing an HF solution may be used.

Next, the first contact electrode 3A and the wiring pattern 3C areformed on the insulating layer 16 by a vapor-deposition technique. Inthe formation of these, first, a predetermined resist pattern is formedon the insulating layer 16 by a technique of photolithography, and next,an electrode material is vapor-deposited on the insulating layer 16 withthis resist pattern serving as a mask. Here, in place of avapor-deposition technique, a sputtering method may be used.

Next, as shown in FIG. 12B, the insulating layer 17 is formed on theinsulating layer 16. The insulating layer 17 may be formed by use of asputtering method or a plasma CVD method. In the case where a plasma CVDmethod is used, tetraethoxysilane (TEOS) and oxygen gas are used as rawmaterial gases, and the growth temperature is set to approximately 200°C., to carry out the growth of the insulating layer 17. The thickness ofthe insulating layer 17 is preferably set to a thickness in which it ispossible to planarize its surface, and is preferably higher than aheight from the surface of the insulating layer 16 to the top surface ofthe wiring pattern 3C.

Next, as shown in FIG. 12C, the resistive part 4 is formed on theinsulating layer 17. In the formation of this, first, a predeterminedresist pattern is formed on the insulating layer 17 by a technique ofphotolithography, and next, a resistance material is deposited on theinsulating layer 17 by use of a sputtering method or a vapor-depositiontechnique by using this resist pattern serving as a mask. In the casewhere the resistive element is made of SiCr, a sputtering method isused, and as a target material, for example, SiCr with a compositionratio of Si and Cr of 70%/30% may be used, and the thickness may be setto 3 to 50 nm.

In addition, in the case where the light detecting sections having thestructure shown in FIG. 13 is manufactured, it is recommended that thesemiconductor region 15 be formed on the surface side of thesemiconductor region 13 by use of an impurity diffusion method or an ionimplantation method before the formation of the semiconductor region 14.In the case of an impurity diffusion method, impurities corresponding tothe conductivity type of the semiconductor region 15 are diffused as gasor solid in the semiconductor region 13. In the case of an ionimplantation method, impurities corresponding to the conductivity typeof the semiconductor region 15 are ion-implanted into the semiconductorregion 13.

In addition, in the case of the above-described embodiment, the planarshape of the resistive layer 4B is a shape of a part of an annular orring shape, or a spiral form. However, this may be a meandering shapelike a square wave, a triangle wave, or a sine wave.

Further, the effects of the photodiode array according to the embodimentwill be further described.

In the case where the photodiode array is operated in the Geiger mode, arecovery time (voltage recovery time) τ in the case where photons aremade incident to the one light detecting sections 10 depends on aproduct (RC constant=Cj×Rq) of a junction capacitance (pixel capacity)Cj stipulated by an area of the light detection region in the lightdetecting sections 10 and a depletion layer width expanding from the p-njunction, and a resistance value of the resistive part 4 (quenchingresistance value Rq).

When the pixel size (the area of the light detecting sections) is madesmaller, the junction capacitance Cj becomes smaller. Therefore, inorder to obtain the same recovery time τ, i.e., the same RC constant, itis necessary to increase the quenching resistance value Rq. Thequenching resistance value Rq may be determined by adjusting theresistivity, the thickness, the width, and the length. Because theresistivity, the width, and the thickness are restricted by processconditions, it is rational that the resistance value Rq is adjusted bychanging the length. In order to obtain the same recovery time z, thelarger the pixel size is, the resistive layer 4B is set to be shorter,and the smaller the pixel size is, the resistive layer 4B is set to belonger.

In the case where the RC constant is too small, quenching afteroccurrence of avalanche multiplication is made insufficient, and aphenomenon called latching current is caused, that does not indicate anormal operation. On the other hand, in the case where the RC constantis too large, the recovery time (voltage recovery time) gets longer.Accordingly, a value of the RC constant is set to an optimum value (2 to20 nm) according to a device.

In addition, the gain depends on the junction capacitance Cj and anapplied voltage, and in the structure of the embodiment, the gain isdecreased by reducing the junction capacitance Cj. As a noise componentof the photodiode array, in addition to a dark pulse, an after pulse,and a pseudo-output signal by an optical crosstalk as well are included.An after pulse means a pulse which is generated such that some of theelectrons/holes generated by avalanche multiplication are trapped by animpurity level or the like, and are thereafter released at a certaintime interval, thereby causing avalanche multiplication again. Anoptical crosstalk is caused by a pulse which is generated such thatphotons generated with a low probability during avalanche multiplicationenter into an adjacent pixel to be absorbed therein, to generate pairsof electrons/holes, thereby causing avalanche multiplication. The bothare noise components by which the output for one photon is not onepulse, but a plurality of pulses.

As in the structure of the embodiment, when the junction capacitance Cj,i.e., the gain is little, the total number of pairs of electrons/holesgenerated by avalanche multiplication is made smaller, the probabilityof generation of pulses by an after pulse and an optical crosstalk islowered, which makes it possible to obtain an effect of noise reduction.

Because the large junction capacitance Cj and the higher gain theelement has, the longer the time of sweeping out the generated carriersis, the voltage recovery time gets longer. The lower the gain is, therecovery time gets shorter. As in the embodiment, when the pixel pitchis made smaller, the voltage recovery time gets shorter, which makes itpossible to improve the photon counting rate.

What is claimed is:
 1. A photodiode array comprising: avalanchephotodiodes; an insulating layer provided at a light incident side of asemiconductor substrate, covering the avalanche photodiodes; andquenching resistors respectively connected to the avalanche photodiodes,each quenching resistor being provided on the insulating layer andarranged to cover an edge of a semiconductor region that forms one sideof each avalanche photodiode, wherein each of the quenching resistorsincludes: an upper surface, a lower surface, and side surfaces extendingalong a surface of the insulating layer in a plan view, a strip of thequenching resistor defined by the side surfaces and forming a ring-likestrip shape in the plan view.
 2. The photodiode array according to claim1, wherein the quenching resistor comprises SiCr.
 3. The photodiodearray according to claim 2, wherein a thickness of a resistive layer ofthe quenching resistor is 3 nm or more and 50 nm or less.
 4. Thephotodiode array according to claim 3, wherein the resistive layer hastransmittance of 80% or more with respect to light with a wavelengthranging from 400 nm to 1200 nm, and the semiconductor substrate formingthe avalanche photodiodes comprises Si.
 5. The photodiode arrayaccording to claim 1, wherein an interval X between centers of adjacentlight detecting sections is 20 μm or less, the light detecting sectionsincluding the avalanche photodiodes respectively.
 6. The photodiodearray according to claim 1, wherein a sheet resistance of a resistivelayer of the quenching resistor is in a range from 1 to 50 (kΩ/sq.). 7.The photodiode array according to claim 1, wherein the avalanchephotodiodes are operated in Geiger mode, and the avalanche photodiodecauses a voltage drop in the quenching resistor when an avalanche effectoccurs in the avalanche photodiode.